Another Look at DC Power

April 25, 2012

Back in December, I posted a note about the resurgence of interest in DC power distribution systems, especially within data centers.  Although large scale electricity distribution systems (such as regional or national grids) have used AC for years, since the resolution of the “War of the Currents“,and obviously constitute a workable solution — I am, after all, writing this at about 10:00 PM — the data center environment differs in some significant ways from that of the average utility customer.  The electronic devices themselves almost all work on DC power  (converted from the AC supplied by the grid; backup power supplies for emergencies almost always use batteries, which supply DC.   As I noted in that earlier post, the use of DC distribution in large data centers could potentially produce significant increases in energy efficiency.

Technology Review has a new article that discusses the possible use of DC power distribution on a larger scale.   According to Greg Reed, director of the Power & Energy Initiative at the University of Pittsburgh, the growth in the use of electronic devices, especially consumer electronic devices, has meant that a larger amount of the total demand for power is, ultimately, for DC.  Currently, this DC power is supplied by the battery chargers, power supplies, and “wall warts” of our PCs, smart phones, flat-screen TVs, and other gadgets.  Reed thinks that this trend will continue.

“Within the next 20 years we could definitely see as much as 50 percent of our total loads be made up of DC consumption,” he [Reed] says. “It’s accelerating even more than we’d expected.”

He goes on to argue that a “DC takeover” of the grid is “inevitable”, due to improvements in efficiency, from eliminating AC/DC conversions, and to the increased use of consumer electronics, solar panels, and LED lighting, all of which are more “at home” in a DC-powered world.

It is certainly true that there is technology today, unavailable in Edison’s time, that makes high-voltage DC transmission over significant distances feasible.  I expect this type of distribution will be used more in the future for installations where it makes sense.  I also think that the use of DC power distribution in data centers will increase; moreover, this kind of local grid installation probably makes sense in a number of other contexts, like large commercial buildings.  Electric vehicles, too, use batteries that are recharged with DC power, so there is probably a role for local DC grids there.

Dragan Maksimovic, an expert in power electronics at the University of Colorado in Boulder, estimates that solar-powered vehicle chargers his group is developing should cut power losses from 10 percent of what the panels produce to just 2 percent.

So, I think there is a pretty good case for deployment of DC power distribution on the local scale.  In a data center, it makes little sense to have a large number of servers, each with its own power supply, taking AC from the local utility and turning it into, say, 24 volt DC.  However, I very much doubt that we will see any wholesale switch to DC power distribution on a large scale.  The US power grid represents a huge capital investment, and it does work.

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